Densifying Carbon Dioxide With a Dispersion of Carbon Dioxide-Philic Water Capsules

ABSTRACT

This invention generally relates to the field of oil recovery from reservoirs. More specifically, it relates to the recovery of oil from sandstone and carbonate reservoirs using a process for preparing a dispersion of capsules for use downhole including the steps of providing capsules containing a dense liquid, each capsule having a capsule wall defining an inner area, the capsule wall having an outer side. The capsules are functionalized by adding a carbon dioxide-philic compound compound to the outer side of the capsule wall. A dispersion is then prepared by adding the functionalized capsules to supercritical carbon dioxide such that a stable dispersion of capsules in supercritical carbon dioxide is achieved.

This application claims priority to U.S. Provisional Application Ser.No. 61/725,183 filed on Nov. 12, 2012, which is incorporated byreference in its entirety.

FIELD OF INVENTION

This invention generally relates to the field of oil recovery fromreservoirs. More specifically, it relates to the recovery of oil fromsandstone and carbonate reservoirs.

BACKGROUND

Carbon dioxide flooding processes are an important enhanced oil recoverymethod to recover oil from both sandstone and carbonate reservoirs.Approximately one third of the original oil in place is recovered byprimary and secondary recovery processes. However, this typically leavestwo-thirds of the oil trapped in reservoirs as residual oil after waterflooding. An additional 5-20% of the oil may be recovered by carbondioxide flooding processes. However, increasing the recovery beyond thishas remained difficult because of several challenges. First is thegravity override of the injected carbon dioxide due to densitydifferences between the injected carbon dioxide and resident fluids inthe reservoir. The carbon dioxide, being lighter, tends to rise to thetop of the reservoir thereby bypassing some of the remaining oil, Thisresults in poor oil recovery in the lower portion of the reservoir. Thisproblem is especially acute in thick formations. The second challenge isviscous fingering that is caused by the lower viscosity of the injectedcarbon dioxide. Typical dense carbon dioxide viscosity at reservoirconditions is in the range of 0.05-0.1 cP, which is much lower than theviscosity of resident oil and brine. The resulting unfavorable mobilityratio leads to viscous fingering. This causes early carbon dioxidebreakthrough, high carbon dioxide utilization factors, poor sweepefficiency, and low overall oil recoveries. The third challenge isreservoir geology and heterogeneities, including high permeabilitystreaks and fractures that can affect the sweep efficiency of a carbondioxide enhanced oil recovery flooding processes. Whilewater-alternating-gas processes have shown to improve the mobility ofcarbon dioxide somewhat, water-alternating-gas processes have notcompletely overcome these challenges.

Increasing the density and viscosity of carbon dioxide can alleviatemany of these challenges and lead to substantial higher recovery thanconventional carbon dioxide enhanced oil recovery processes. Carbondioxide density can be increased by blending in heavier compatiblematerials. However, limited success has been achieved using thisapproach, partly because the densities of the molecules that havepreviously been used are not high enough.

Additionally, known methods use surfactants to foam or to create waterin carbon dioxide reverse micelles. While creating a foam addresses thechallenge of viscosity, it leaves the challenge of density unresolved.Although research results have demonstrated that surfactant-inducedcarbon dioxide foams are an effective method for mobility control incarbon dioxide foam flooding, the foam's long-term stability during afield application is difficult to maintain.

Moreover, even if a carbon dioxide thickener, whether a polymer or smallmolecule, is identified, operational constraints may face operators whowould try to implement the technology in a pilot-test. Nearly allpotential carbon dioxide thickeners are a solid at ambient temperatureand a means of introducing a powder into the carbon dioxide stream mustbe employed, possibly by first dissolving the thickener in an organicsolvent in order to form a concentrated, viscous, pumpable solution.

Reverse micelles carry a small amount of water with a significant amountof surfactant due to the nature of micelles. In other words, micellescarry little payload due to their high surface to volume ratios.

A capsule based carbon dioxide system addresses the density challenge bydelivering a substantial amount of a dense liquid, such as water orheavy filler. The surface-volume ratio of the capsule is much smallerthan that of reverse micelle, hence more payload can be added to thecapsule based carbon dioxide system and more density increase can berealized using such a system.

A capsule based carbon dioxide system also addresses the viscositychallenge because of the drag force of carbon dioxide on the capsules,and the inherent viscosity of carbon dioxide-philic molecules on thecapsules.

SUMMARY OF THE INVENTION

The features and advantages of the present invention will be readilyapparent to those skilled in the an upon a reading of the description ofthe preferred embodiments that follows.

Some embodiments of the invention are related to a process for preparinga dispersion of capsules for use downhole including providing capsulescontaining a dense liquid. Each capsule has a capsule wall that definesan inner area. The capsule wall also has an outer side. The capsules arefunctionalized by adding a carbon dioxide-philic compound to the outerside of the capsule wall. A dispersion is then prepared by adding thefunctionalized capsules to supercritical carbon dioxide such that astable dispersion of capsules in supercritical carbon dioxide isachieved.

A stable capsule dispersion that is useful for enhanced oil recoveryincludes a disperse phase of a plurality of functionatized capsules.Each functionalized capsule contains the dense liquid in an inner areawithin the capsule wall. Each functionalized capsule is operable to bestably dispersed within supercritical carbon dioxide. The capsule wallof each functionalized capsule defines the inner area and has an outerside functionalized with a carbon dioxide-philic compound. The stablecapsule dispersion also includes a continuous phase of supercriticalcarbon dioxide. The stable capsule dispersion has a density that isgreater than the density of supercritical carbon dioxide at the sameconditions (that is, temperature, pressure). The stable capsuledispersion also has a viscosity that is greater than the viscosity ofsupercritical carbon dioxide at the same conditions.

In some embodiments of the invention, the capsules are prepared by aprocess that includes providing a second liquid that is operable to forma liquid phase when combined with the dense liquid. A first monomer isadded to the dense liquid to create a monomer-liquid composition. Asecond monomer is added to the second liquid to create a secondmonomer-liquid composition. The monomer-liquid composition is added tothe second monomer-liquid composition and agitated to create adispersion of monomer-liquid composition with the second. monomer-liquidcomposition such that intimate mixing is achieved. The agitationcontinues for a pre-determined amount of time such that polymerizationof the first and second monomers is achieved at the liquid-liquidinterface and capsules are formed.

Another embodiment of the invention is a process for enhancing oilrecovery. The process includes providing capsules containing a denseliquid, each capsule having a capsule wall defining an inner area, thecapsule wall having an outer side. The capsules are functionalized byadding a carbon dioxide-philic compound to the outer side of the capsulewall to create functionalized capsules. A capsule dispersion is thenprepared by adding the functionalized capsules to supercritical carbondioxide such that a stable dispersion of capsules in supercriticalcarbon dioxide is achieved with the stable dispersion having a densitygreater than supercritical carbon dioxide. The stable dispersion ofcapsules in supercritical carbon dioxide is then injected into areservoir. Because the density of the stable dispersion of capsules insupercritical carbon dioxide is greater than the density ofsupercritical carbon dioxide alone, the injection will flood thereservoir more uniformly than supercritical carbon dioxide alone.Additionally, the injection should reduce viscous fingering of thesupercritical carbon dioxide, increase sweep efficiency, and reduceearly carbon dioxide breakthrough.

A further embodiment to the invention is a process for preparing adispersion of capsules. The capsules contain a heavy liquid filler. Eachcapsule has a capsule will that defines an inner area. The capsule wallalso has an outer side. The capsules are functionalized by adding acarbon dioxide-philic compound to the outer side of the capsule wall. Adispersion is then prepared by adding the functionalized capsules tosupercritical carbon dioxide such that a stable dispersion of capsulesin supercritical carbon dioxide is achieved.

In a further embodiment, a liquid capsule is prepared using a hydrogel.Water or heavy liquid can be stored in the hydrogel. The hydrogel basedparticles or capsules are functionalized by adding a carbondioxide-philic compound to the outer side of the hydrogel capsule.

BRIEF DESCRIPTION OF DRAWINGS

So that the manner in which the features and advantages of theinvention, as well as others that will become apparent, may beunderstood in more detail, a more particular description of theinvention briefly summarized above may be had by reference to theembodiments thereof, which are illustrated in the appended drawings,which form a part of this specification. It is to be noted, however,that the drawings illustrate only various embodiments of the inventionand are therefore not to be considered limiting of the invention's scopeas it may include other effective embodiments as well.

FIG. 1 is a drawing of a carbon dioxide enhanced oil recovery systemknown in the art.

FIG. 2 shows that reservoir geology and heterogeneities can include highpermeability streaks and fractures that can affect the sweep efficiencyof a carbon dioxide enhanced oil recovery flood.

FIG. 3 shows a schematic of the carbon dioxide-philic capsule systemaccording to an embodiment of the claimed invention.

DETAILED DESCRIPTION

Embodiments of the invention are related to a process for preparing adispersion of capsules for use downhole including the steps of providingcapsules containing a dense liquid. Each capsule has a capsule wail thatdefines an inner area. The capsule wall also has an outer side. Thecapsules are functionalized by adding a carbon dioxide-philic compoundto the outer side of the capsule wall. A dispersion is then prepared byadding the functionalized capsules to supercritical carbon dioxide suchthat a stable dispersion of capsules in supercritical carbon dioxide isachieved.

A “dispersion” is a two-phase system where one phase consists of finelydivided particles (often in the colloidal size range) that isdistributed throughout a bulk substance, where the particles are thedisperse or internal phase and the bulk substance the continuous orexternal phase. Solid-in-liquid colloidal dispersions (loosely calledsolutions) can be precipitated, in that larger particles will graduallycoalesce and either rise to the top or settle out, depending on theirspecific gravity relative to the bulk substance.

In some embodiments of the invention, the capsules are prepared by aprocess that includes providing a second liquid that is operable to forma liquid phase when combined with the dense liquid. A first monomer isadded to the dense liquid to create a monomer-liquid composition. Asecond monomer is added to the second liquid to create a secondmonomer-liquid composition. The monomer-liquid composition is added tothe second monomer-liquid composition and agitated to create adispersion of monomer-liquid composition with the second monomer-liquidcomposition such that intimate mixing is achieved, The agitationcontinues for a pre-determined amount of time such that polymerizationof the first and second monomers is achieved at the liquid-liquidinterface and capsules are formed. In further embodiments, the secondliquid and the dense aqueous liquid are the same.

An embodiment of the invention is a process for enhancing oil recovery.The process includes providing capsules containing a dense liquid, eachcapsule having a capsule wall defining an inner area, and the capsulewall having an outer side. The capsules are functionalized by adding acarbon dioxide-philic compound to the outer side of the capsule wall tocreate functionalized capsules. A capsule dispersion is then prepared byadding the functionalized capsules to supercritical carbon dioxide suchthat a stable dispersion of capsules in supercritical carbon dioxide isachieved with the stable dispersion having a density greater thansupercritical carbon dioxide. The stable dispersion of capsules insupercritical carbon dioxide is then injected into a reservoir. Becausethe density of the stable dispersion of capsules in supercritical carbondioxide is greater than the density of supercritical carbon dioxidealone, the injection will flood the reservoir more uniformly thansupercritical carbon dioxide alone. Additionally, the injection shouldreduce viscous fingering of the supercritical carbon dioxide, increasesweep efficiency, and reduce early carbon dioxide breakthrough.

The present invention will improve the recovery of oil over traditionalenhanced oil recovery systems by enhancing recovery of oil from bypassedzones, For instance, FIG. 1 is a drawing of a traditional carbon dioxideenhanced oil recovery system. In the previously known systems, such asthe one shown in FIG. 1, there is a gravity override, whereby the carbondioxide injected at injection well 100 rises as a gas sweep 110, a watersweep 120 occurs below the gas sweep, and oil containing regions arecompletely untouched by the carbon dioxide. This results in a bypassedzone 130 from which oil is not fully recovered by the production at well140. Embodiments of the present invention reduce or eliminate thebypassed zone 130. This is accomplished by increasing the density of thesupercritical carbon dioxide and thus reducing the gravity override thatis experienced within the system. Additionally, the viscosity of thesupercritical carbon dioxide will be increased.

The capsule-based carbon dioxide system of the present inventionaddresses the viscosity challenge associated with traditional enhancedoil recovery systems because of the drag force of carbon dioxide on thecapsules, and the inherent viscosity of carbon dioxide-philic moleculeson the capsules in the present invention. This overcomes the viscousfingering of the traditional carbon dioxide enhanced oil recoverysystems. Viscous fingering this caused by the lower viscosity ofinjected carbon dioxide in traditional carbon dioxide enhanced oilrecovery processes. The present invention will reduce this fingeringeffect by increasing the viscosity of the supercritical carbon dioxidethat is injected into a well, thus increasing the oil recovery from agiven well.

The present invention will also address the reservoir geology andheterogeneities issues of wells. As shown in FIG. 2, reservoir geologyand heterogeneities can include high permeability streaks and fracturesthat can affect the sweep efficiency of a carbon dioxide enhanced oilrecovery process. As shown in FIG. 2, which is a typical porosity v,permeability plot, as porosity increases, permeability increases, Whilethe data shown in FIG. 2 as obtained for a reservoir in Saudi Arabia,the same general trend should be seen in other reservoirs as well. Thepresent invention will address these issues by increasing the densityand viscosity of the supercritical carbon dioxide, thus increasing thesweep efficiency of the carbon dioxide oil recovery process.

In further embodiments, the dense liquid of the present invention isnon-supercritical at downhole operating pressure and temperature. Infurther embodiments, the dense liquid has a density of at least about0.5 g/cc (grams per cubic centimeter). In further embodiments, thepreferred dense liquid has density of at least about 0.55 g/cc. Infurther embodiments, the preferred dense liquid has density of at aboutleast 0.60 g/cc. Preferred dense liquids include water, but can alsoinclude any other liquids which will have limited. environmental impactand which will not impede recovery of oil from a well, In someembodiments, the dense liquid is a dense aqueous liquid.

In further embodiments, the dense liquid is a heavy liquid filler. Thefiller can include any variety of heavy liquid filler but particularlypreferred. heavy liquid fillers have densities of at least about 0.5g/cc. In further embodiments, preferred heavy liquid tillers havedensities of at least about 0.55 g/cc. In further embodiments, thepreferred heavy liquid fillers have densities of at least about 0.60g/cc. Additionally, in some embodiments, the heavy liquid filler willhave limited environmental impact. In some embodiments, the heavy liquidfillers are selected from toluene, crude oil, ester, silicone oil,alcohols, acetone, and the like.

The first monomer can be any monomer capable of reacting with the secondmonomer to form a co-polymer capsule that can be functionalized withcarbon dioxide-philic compounds. In preferred embodiments, the firstmonomer is an amine. In particularly preferred embodiments, the firstmonomer is triethylene tetramine. In other embodiments, the firstmonomer is selected from hexamethylene tetramine, ethylene diamine,hexamethylene diamine, diethylene triamine, and the like.

The second monomer can be any monomer capable of reacting with the firstmonomer to form a co-polymer capsule that can be functionalized withcarbon dioxide-philic compounds. In preferred embodiments, the secondmonomer is an isocyanate. In particularly preferred embodiments, theisocyanate is polymeric diphenylmethane diisocyanate. In a preferredembodiment, the polymeric diphenylmethane diisocyanate is Mondur® MRS.In some embodiments, the second monomer is selected from isophoronediisocyante, Mondur® 489, hexamethylene diisocyanate, 1,4 phenylenediisocyanate, toluene 2,4 diisocyanate, and the like.

Carbon dioxide-philic compounds include fluorine containing compoundssuch as perfluoroethers, fluoroalkyls, fluoroacrylates, fluoroalkanes,and fluoroethers; silicon containing compounds including siloxanes, suchas polydimethylsiloxane, and silicones; oxygenated hydrocarbon compoundssuch as propylene oxides; and other hydrocarbons such as polyvinylacetate. Particularly preferred carbon dioxide-philic compounds includefluorinated carbon dioxide-soluble surfactant and oxygenated hydrocarboncarbon dioxide-philic molecules. In some embodiments, the carbondioxide-philic compound is poly (1,1 dihydroperfluoroctyl acrylate).

A further embodiment of the invention is a process for preparing adispersion of capsules. The capsules contain a heavy liquid filler thatis heavier than carbon dioxide. Each capsule has a capsule wall thatdefines an inner area. The capsule wall also has an outer side. Thecapsules are functionalized by adding a carbon dioxide-philic compoundto the outer side of the capsule wall. A dispersion is then prepared byadding the functionalized capsules to supercritical carbon dioxide suchthat a stable dispersion of capsules in supercritical carbon dioxide isachieved.

The capsules resulting from the processes described herein are operableto be stably dispersed in supercritical carbon dioxide, The resultingoverall density of the supercritical carbon dioxide increases as aresult of the stable dispersion of the capsules therein. Additionally,the dispersion of capsules in the supercritical carbon dioxide increasesthe viscosity of the supercritical carbon dioxide.

The dispersion of capsules in supercritical carbon dioxide increases theviscosity of the supercritical carbon dioxide due to the drag force ofcarbon dioxide on the capsules, and the inherent viscosity of carbondioxide-philic molecules on the capsules. A conceptual drawing of thecarbon dioxide-philic compounds attached to the outer side of thecapsule wall is shown in FIG. 3. As shown in FIG. 3, there is a fillingin the inner area 200. in some embodiments, the filling is water orother dense liquid. Surrounding the inner area is a polymer capsuleshell 210. Attached to the polymer capsule shell are carbondioxide-philic functional groups 230. These capsules are dispersed insupercritical carbon dioxide.

According to some embodiments, the capsules are nano-scale. Nano-scalecapsules according to the invention can range in size from about 110nanometers to about 11,000 nanometers, Nano-scale capsules according tothe invention can range in size from about 0.1 nanometers to about 1,000nanometers. In some embodiments, the nano-scale capsules according tothe invention can range in size from about 5 nanometers to about 500nanometers, In some embodiments, the nano-scale capsules according tothe invention can range in size from about 50 nanometers to about 250nanometers. In some embodiments, the nano-scale capsules according tothe invention can range in size from about 100 nanometers to about 200nanometers, in some embodiments, the capsules are of uniform size. Infurther embodiments, the capsules are of uniform size such that the sizeof the capsules does not vary by more than about 30% percent. In otherembodiments, the capsules are not of uniform size.

According to other embodiments, the capsules are micro-scale.Micro-scale capsules according to the invention can range in size fromabout 0.01 micrometers to 1,000 micrometers, In some embodiments, themicro-scale capsules according to the invention can range in size fromabout 5 micrometers to about 500 micrometers. In some embodiments, themicro-scale capsules according to the invention can range in size fromabout 50 micrometers to about 250 micrometers. In some embodiments, themicro-scale capsules according to the invention can range in size fromabout 100 micrometers to about 200 micrometers. In some embodiments, thecapsules are of uniform size. In further embodiments, the capsules areof uniform size such that the size of the capsules does not vary by morethan about 30% percent. In other embodiments, the capsules are not ofuniform size.

In a further embodiment, a liquid capsule is prepared using a hydrogel.The hydrogel based particles or capsules are functionalized by adding acarbon dioxide-philic compound to the outer side of the hydrogelcapsule. The particles or capsules can be made of any suitable hydrogelmaterial, including gelatin, chitosan, starch, alginate, polyvinylalcohol, polyethylene oxide, polyvinyl pyrrolidone, and polyisopropylacrylamide. Hydrogel particles can be formed by various techniques. Forexample, chitosan can be dissolved in acidic water and then thedissolved chitosan can be forced to precipitate out in basic solution.The precipitate can be in the form of particles with a wide range ofdiameters, depending on experimental conditions. A crosslinking agentcan then be introduced to ensure the integrity of the chitosanparticles. The chitosan particles are hydrogel particles given theamount of water absorbed by the chitosan particles.

Embodiments of the present invention may suitably comprise, consist orconsist essentially of the elements disclosed and may be practiced inthe absence of an element not disclosed. For example, it can berecognized by those skilled in the art that certain steps can becombined into a single step.

Unless defined otherwise, all technical and scientific terms used havethe same meaning as commonly understood by one of ordinary skill in theart to which this invention belongs.

The singular forms “a,” “an,” and “the” include plural referents, unlessthe context clearly dictates otherwise.

As used herein and in the appended claims, the words “comprise,” “has,”and “include” and all grammatical variations thereof are each intendedto have an open, non-limiting meaning that does not exclude additionalelements or steps.

Ranges may be expressed herein as from about one particular value,and/or to about another particular value. When such a range isexpressed, it is to be understood that another embodiment is from theone particular value and/or to the other particular value, along withall combinations within said range.

Although the present invention has been described in detail, it shouldbe understood that various changes, substitutions, and alterations canbe made hereupon without departing from the principle and scope of theinvention. Accordingly, the scope of the present invention should bedetermined by the following claims and their appropriate legalequivalents.

The invention claimed is:
 1. A process for preparing dispersion ofcapsules for use downhole comprising the steps of: providing capsulescontaining a dense liquid, each capsule having a capsule wall definingan inner area, the capsule wall having an outer side; functionalizingthe capsules by adding a carbon dioxide-philic compound to the outerside of the capsule wall to create functionalized capsules; preparing adispersion by adding the functionalized capsules to supercritical carbondioxide such that a stable dispersion of capsules in supercriticalcarbon dioxide is achieved.
 2. A process according to claim 1, whereinsaid capsules are prepared by a process comprising the steps of:providing a second liquid, the second liquid operable to form a liquidphase when combined with the dense liquid; adding a first monomer to thedense liquid to create a monomer-liquid composition; adding a secondmonomer to the second liquid to create a second monomer-liquidcomposition; adding the monomer-liquid composition to the secondmonomer-liquid composition; agitating the monomer-liquid composition andthe second monomer-liquid composition to create a dispersion ofmonomer-liquid composition with the second monomer-liquid compositionsuch that intimate mixing is achieved, the agitation continuing for apre-determined amount of time such that polymerization is achieved andcapsules are formed.
 3. The process according to claim 1, wherein saiddense liquid is non-supercritical at downhole operating pressure andtemperature.
 4. A process according to claim 1, wherein the dense liquidhas a density of at least about 0.5 g/cc (grams per cubic centimeter).5. The process of claim 4 wherein the dense liquid is water.
 6. Aprocess according to claim 2, wherein the first monomer comprisestriethylene tetramine.
 7. A process according to claim 2, wherein thesecond monomer comprises Mondur® MRS.
 8. A process according to claim 1,wherein the carbon dioxide-philic compound comprises fluorinated carbondioxide-soluble surfactant or oxygenated hydrocarbon carbon dioxidephilic molecules.
 9. A process for enhancing oil recovery comprising thesteps of: providing capsules containing a dense liquid, each capsulehaving a capsule wall defining an inner area, the capsule wall having anouter side; functionalizing the capsules by adding a carbondioxide-philic compound to the outer side of the capsule wall to createfunctionalized capsules; preparing a capsule dispersion by adding thefunctionalized capsules to supercritical carbon dioxide such that astable dispersion of capsules in supercritical carbon dioxide isachieved with the stable dispersion having a density greater thansupercritical carbon dioxide; and injecting the stable dispersion ofcapsules in supercritical carbon dioxide into a reservoir.
 10. A processaccording to claim 9, wherein said capsules are prepared by a processcomprising the steps of providing a second liquid, the second liquidoperable to form a second liquid phase when combined with the denseliquid; adding a first monomer to the dense liquid to create amonomer-liquid composition; adding a second monomer to the second liquidto create a second monomer-liquid. composition; adding themonomer-liquid composition to the second monomer-liquid composition;agitating the monomer-liquid composition and the second monomer-liquidcomposition to create dispersion of monomer-liquid composition in thesecond monomer-liquid composition; and allowing the first and secondmonomers to diffuse and to polymerize such that capsules are formed. 11.The process according to claim 9, wherein said dense liquid isnon-supercritical at downhole operating pressure and temperature.
 12. Aprocess according to claim 9, wherein the dense liquid has a density ofat least about 0.5 g/cc.
 13. A process according to claim 10, whereinthe first monomer comprises triethylene tetramine.
 14. A processaccording to claim 10, wherein the second monomer comprises Mondur® MRS.15. A process according to claim 9, wherein the carbon dioxide-philiccompounds comprises fluorinated carbon dioxide-soluble surfactant oroxygenated hydrocarbon carbon dioxide-philic molecules.
 16. The processof claim 9 further comprising injecting water into the reservoir. 17.The process of claim 9 further comprising injecting a second amount ofstable dispersion of capsules in supercritical carbon dioxide into thereservoir.
 18. The process of claim 17 further comprising injecting athird amount of stable dispersion of capsules in supercritical carbondioxide into the reservoir.
 19. The process of claim 9 wherein the denseliquid further comprises a heavy liquid filler.
 20. A process forpreparing a dispersion of capsules comprising: providing capsulescontaining a heavy liquid filler, each capsule having a capsule walldefining an inner area, the capsule wall having an outer side;functionalizing the capsules by adding a carbon dioxide-philic compoundto the outer side of the capsule wall to create functionalized capsules;preparing a dispersion by adding the functionalized capsules tosupercritical carbon dioxide such that a stable dispersion of capsulesin supercritical carbon dioxide is achieved.
 21. A stable capsuledispersion that is useful for enhanced oil recovery, the stable capsuledispersion comprising: a disperse phase of a plurality of functionalizedcapsules, where each functionalized capsule contains a dense liquid inan inner area within a capsule wall and is operable to be stablydispersed within supercritical carbon dioxide, where the capsule wall ofeach functionalized capsule defines the inner area and has an outer sidefunctionalized with a carbon dioxide-philic compound; and a continuousphase of supercritical carbon dioxide; such that the density of thecapsule dispersion is greater than the density of supercritical carbondioxide at the same conditions and such that the viscosity of thecapsule dispersion is greater than the viscosity of supercritical carbondioxide at the same conditions.
 22. The capsule dispersion of claim 21where the dense liquid has a density of at least about 0.5 g/cc.
 23. Thecapsule dispersion of claim 21 where the functionalized capsules have asize in a range of from about 110 nanometers to about 11,000 nanometers.24. The capsule dispersion of claim 21 where the dense liquid is a denseaqueous liquid.
 25. The capsule dispersion of claim 21 where the denseliquid is a heavy liquid filler selected from the group consisting oftoluene, crude oil, ester, silicone oil, alcohols, acetone, andcombinations thereof.
 26. The capsule dispersion of claim 21 where thecapsule wall of each functionalized capsule is composed of a co-polymerthat is the polymerization product of a first co-monomer and a secondco-monomer.
 27. The capsule dispersion of claim 26 where the firstmonomer is selected from the group consisting of triethylene tetramine,hexamethylene tetramine, ethylene diamine, hexamethylene diamine,diethylene triamine, and combinations thereof.
 28. The capsuledispersion of claim 26 where the second monomer is selected from thegroup consisting of polymeric diphenylmethane diisocyanate, isophoronediisocyante, hexamethylene diisocyanate, 1,4 phenylene diisocyanate,toluene 2,4 diisocyanate, and combinations thereof.
 29. The capsuledispersion of claim 21 where the capsule wall of each functionalizedcapsule is composed of a hydrogel selected from the group consisting ofgelatin, chitosan, starch, alginate, polyvinyl alcohol, polyethyleneoxide, polyvinyl pyrrolidone, polyisopropyl acrylamide, and combinationsthereof.
 30. The capsule dispersion of claim 21 where the carbondioxide-philic compound is poly (1,1 dihydroperfluoroctyl acrylate).